Undo the split view

Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?

Annotations only declare readOnlyHint=false, so the description carries most of the burden and does so well: 'The two tabs stay open; they just stop sharing the window' is a genuinely non-obvious reassurance that this mutation destroys no user state. It also discloses the return signal (whether a split existed), though it doesn't say whether the no-op case errors or returns false.

Agents need to know what a tool does to the world before calling it. Descriptions should go beyond structured annotations to explain consequences.

Is the description appropriately sized, front-loaded, and free of redundancy?

Three short sentences, front-loaded with the action, then the side-effect scope, then the return value. No boilerplate or repetition of the title.

Shorter descriptions cost fewer tokens and are easier for agents to parse. Every sentence should earn its place.

Given the tool's complexity, does the description cover enough for an agent to succeed on first attempt?

With no output schema and no parameters, the description covers what an agent needs: what is undone, that tabs survive, and that a status is reported. The only gap is the no-split-view edge case (no-op vs. error), which the 'reports whether there was a split view' clause hints at but doesn't resolve.

Complex tools with many parameters or behaviors need more documentation. Simple tools need less. This dimension scales expectations accordingly.

Does the description clarify parameter syntax, constraints, interactions, or defaults beyond what the schema provides?

The tool takes zero parameters, so there is nothing for the description to disambiguate; the baseline of 4 applies. The parenthetical clarifies that it acts on the active tab / current window rather than any specified target, which is the only scoping question that matters here.

Input schemas describe structure but not intent. Descriptions should explain non-obvious parameter relationships and valid value ranges.

Does the description clearly state what the tool does and how it differs from similar tools?

States a specific verb and resource ('Close the split view in the current window'), and the parenthetical implementation reference (gBrowser.unsplitView on the active tab) pins the exact scope. It is unambiguously the inverse of the browser_split_view sibling, so an agent can tell them apart without inspecting schemas.

Agents choose between tools based on descriptions. A clear purpose with a specific verb and resource helps agents select the right tool.

Does the description explain when to use this tool, when not to, or what alternatives exist?

The phrase 'Close the split view' clearly signals the condition (a split view exists and should be undone) and implies the counterpart tool. However, it never names browser_split_view or states what happens if no split view is active, so the routing is inferred rather than explicit.

Agents often have multiple tools that could apply. Explicit usage guidance like "use X instead of Y when Z" prevents misuse.